The present invention relates to a hand prosthesis or prosthetic prehensor for use by an amputee.
At the present time, arm amputees have a basic choice of a hook or an artificial hand for the prosthetic prehensor. There are compromises between these two options. The hook is more functional, and the hand is more cosmetic.
A typical hook is shown in FIG. 1. The hook has two hook bars 10 and 12. Hook bar 10 is stationary while hook bar 12 is moved about a pivot 14 by a cable 16 pulling on a member 18. Cable 16 is typically attached to a harness to the amputee's shoulder, and the hook is opened by shrugging the shoulder. The hook shown is the voluntary opening (VO) type, and is closed by the action of a spring in the form of a resilient band 20. Other types of prosthetic prehensors may be of the voluntary closing (VC) type. The VC type is more mechanically complex and less frequently used. The hook of FIG. 1 has the advantages that it is light weight, the object being grasped can be seen, the construction is mechanically simple, it is compact enough to get into pockets and is versatile.
A second type of hand prothesis is shaped to look like a human hand and does not actually move. A mechanical hand prothesis is shown in FIG. 2. Most mechanical hands are designed with 3- point prehension using a thumb 22, index finger 24 and a middle finger 26. The remaining two fingers are passive and positionable on some hands, and active and move with the index and middle fingers on others. Most mechanical hands have a grip lock to prevent accidental opening when an object is being carried. The hand is opened by pulling a cable in a similar manner to the hook in FIG. 1. The mechanical mechanisms in the hand are typically covered with a PVC foam material which feels similar to human flesh. In addition, a plastic, cosmetic glove is usually worn over the mechanical hand. The hand is more cosmetic in appearance than the hook, but is heavier, makes it more difficult to see the object being grasped, is mechanically more complex, can not get into pockets and is less versatile than the hook.
Motorized or bionic hands also exist, but are more heavy, complicated and expensive.
Some amputees use two prehensors and interchange them, using a hook for work and the hand for social situations. In addition, there are numerous types of hooks designed for specific tasks.
Many upper-limb amputees who have been queried have expressed a desire for a prehensor which functions as well as a hook but is more aesthetic and less conspicuous looking. A more aesthetic looking prehensor need not be in the shape of a hand.